This research will examine short- and long-term changes in energy expenditure, body composition, body fat distribution, and health status accompanying weight loss (and, in one study, weight regain). Moreover, we will attempt to improve the long-term outcome of the treatment of obesity by exploring the use of exercise to prevent reductions in fat-free mass (FFM) and resting metabolic rate (RMR) which normally occur with weight loss. The proposed research has three specific aims: 1. To assess the adverse effects of weight loss and regain in 119 women who we previously treated for their obesity. We wish to test the hypothesis that weight loss followed by full weight regain is associated with: a) an increased percentage of body fat; b) a lower resting metabolic rate; c) an increased waist-to-hip ratio, indicative of abdominal obesity; and d) increased problem eating, i.e., binge eating. 2. To examine whether exercise--particularly resistance/strength training- -will prevent reductions in FFM and RMR occurring with weight loss and, thus, improve long-term weight control. A total of 128 obese women will be randomly assigned to four conditions: a) diet-alone; b) diet plus aerobic training; c) diet plus resistance/strength training; and d) diet plus combined training (aerobic plus strength training). Subjects will be treated for 1 year and followed for a second. 3. To determine whether weight reduction decreases the energy cost of physical activity, beyond reductions expected with the loss of body weight. Oxygen consumption will be measured in 40 subjects (from the above study) before and after weight loss while performing a constant amount of work on a bicycle ergometer.